package day0220;

public class VerificationDemo {
    public static void main(String[] args) {

        System.out.println(VerificationCode(4));
    }

    public static String VerificationCode(int len){
        String code="";
        char[] ch= {'a','b','c','d','e','f','g','h','i','j','k',
                'l','m','n','o','p','q','r','s','t','u','v',
                'w','x','y','z','A','B','C','D','E','F','G',
                'H','I','J','K','L','M','N','O','P','Q','R',
                'S','T','U','V','W','X','Y','Z','0','1','2',
                '3','4','5','6','7','8','9'};

        for (int i=0;i<len;i++){
            code+=ch[(int)(Math.random()*ch.length)];
        }
        return code;

    }
}